1. Field of the Invention
The present invention relates to a technique for enhancing reliability of a semiconductor device, particularly to a semiconductor device in which durability of a conductive portion against a heat stress generated in an insulating film formed of a low relative dielectric constant film is enhanced.
2. Description of the Related Art
In recent years, to speed up semiconductor devices such as LSI, reduction of a wiring resistance or reduction of dielectric constant of an interlayer insulating film have been advanced. Concretely, a material of a wiring has been shifted to copper (Cu) from aluminum (Al). Also for the interlayer insulating film, films having a low relative dielectric constant film (low-k films) such as a simple SiO2 film, an SiO2 film doped with fluorine, and an SiO2 film containing organic components have been attempted to be employed.
The low relative dielectric constant film is formed by lowering density of the material or by removing polarity from the material. For example, when the material density is lowered, the material is usually prepared to be porous. Since the low relative dielectric constant film is low in the film density, mechanical physical values such as Young's modulus are usually low. That is, the low relative dielectric constant film is weak in the material itself. Additionally, the low relative dielectric constant film includes a film structure having a low polarity so as to lower the dielectric constant in the film. Therefore, adhesion strength is little in a laminate interface between laminate films in which the low relative dielectric constant films are stacked or the low relative dielectric constant film and another film are stacked. Concretely, the materials of the films change in properties by permeation of gas for use in processing/forming via holes or grooves for wirings in the low relative dielectric constant film, or by processing processes. Accordingly, there is possibility that the mechanical strength of the material of the low relative dielectric constant film is deteriorated, or the adhesion strength in the interface between the laminate films including the low relative dielectric constant film is deteriorated.
The little film strength of the low relative dielectric constant film or the little adhesion strength in the interface between the laminate films including the low relative dielectric constant film is a large obstacle to a multi-layer process in which especially the wiring of the semiconductor device is formed in a multi-layered structure. In order to overcome this obstacle, an interface treatment technique or a process at the time of RIE processing is optimized, and accordingly enhancement of the film strength of the low relative dielectric constant film or the adhesion strength in the multi-layered wiring structure including the low relative dielectric constant film has been attempted. This technique is described, for example, in Jpn. Pat. Appln. KOKAI Publication No. 11-176835.
As described above, the material of the low relative dielectric constant film is essentially low in the Young's modulus as compared with that of a general SiO2-based insulating film. Additionally, it is seen that the material of the low relative dielectric constant film is high in coefficient of linear expansion as compared with that of the general SiO2-based insulating film. A possibility that the low Young's modulus and high coefficient of linear expansion of the low relative dielectric constant film cause unknown defects in the semiconductor device and a process for manufacturing the device is high. Additionally, full-scale studies or countermeasures have not been carried out against the low Young's modulus and high coefficient of linear expansion of the low relative dielectric constant film.